Acoustical detecting apparatus

ABSTRACT

Changes in composition of a fluid stream are detected by passing the stream through a chamber having an acoustical signal generator spaced from a detector. The generator is actuated by an oscillator. Signals from the oscillator and the detector are applied to the respective input terminals of a flip-flop circuit. A measurement of the D.C. component of the output signal from the flip-flop circuit provides an indication of changes in composition of the fluid stream.

United States Patent Roof et al. 1 Oct. 2, 1973 [54] ACOUSTICALDETECTING APPARATUS 3,465,264 9/1969 Stone 331/166 3 557 605 l 1971 L tl. 73 24 [75] Inventors: Lewis B. Roof; Harold M. Neer; I anneal] e a IMarvin C. Burk, all of Bartlesville, OTHER PUBLICATIONS kla- Noble etal., Performance and Characteristics of An [73] Assignee: PhillipsPetroleum Company, Ultrasomc Gas Chromatograph Effluent Detector,

Analytical Chemistry, Volume 36, July 1964, pp. Bartlesvrlle, Okla.

1421-1427. [22] Filed: Sept. 14, 1970 Primar ExaminerRichard C. Queisser21 A 1. No.. 72 025 y l 1 pp Assistant ExaminerArthur E. KorkoszAttorney-Young and Quigg [52] US. Cl. 73/24, 73/67.6

[51] Int. Cl. G011] 29/02 57 ABSTRACT [58] Field of Search73/23.1,3224/g;.6A; Changes in Composition of a fluid Stream aredetected by passing the stream through a chamber having an ReferencesCited acoustical signal generator spaced from a detector. The generator15 actuated by an oscillator. Signals from the UNITED STATES PATENTSoscillator and the detector are applied to the respective 2,922,9521/1960 Povey et all 324/83 A input terminals of a flip-flop circuit. Ameasurement of 2,930,895 3/1960 Kuchne 324/83 A X thg component of theutput ignal from the g g l 4 3 flop circuit provides an indication ofchanges in comur e a. 2,963,648 12/1960 Baskin et al. 324/83 A posmon ofthe mud stream 3,211,993 10/1965 Golden et al. 324/83 A 3 Claims, 1Drawing Figure SAMPLE 5 5? CARRIER 47 SAMPLE VALVE 32 CHROMATOGRAPHICCOLUMN 1 46-\ 5 11 :5 DETECTOR 52 0 ST 2 NL; L lCAL 23 28 H U- GENERATOR2| METER sti ma"! PATENTEBUCT 2197} /3 mm 5 .mm W my INVENTORS L. B.ROOF H.M. NEER MC. BURK ATTORNEYS OV mm OMAHA N mOPUmPmQ ACOUSTICALDETECTING APPARATUS Various types of chromatographic analyzers have beendeveloped which are capable of analyzing fluid mixtures. In most ofthese analyzers, a sample of the fluid mixture is introduced into astream of carrier gas which flows through the column. The constituentsof the mixture appear in sequence in the column effluent which is passedto a suitable detecting device. It has recently been found that the useof a carrier liquid in place of the carrier gas can be employed toadvantage in certain separations. However, a need exists for a detectorwhich is capable of accurately measuring small changes in composition ofliquid effluent streams from chromatographic columns.

An acoustical detector which is adapted for use with chromatographicanalyzers is described in US. Pat. No. 3,468,157. The column effluent ispassed through a chamber which has an acoustical generator at one endand a detector at the opposite end. The output signal from an oscillatoris applied to the generator, and the detector measures the signaltransmitted through the chamber. By comparing the oscillator signal withthe detector signal it is possible to observe changes in composition ofthe fluid in the chamber. This is due to changes in the velocity oftransmission of the acoustical signal through the chamber.

In accordance with the present invention, improved apparatus of thegeneral type described in the foregoing patent is provided. A referencesignal from the oscillator is passed through a phase adjustment networkto one input of a flip-flop circuit. The output of the acousticaldetector is passed to the second input of the flip-flop. The flip-flopcircuit provides two output signals which are 180 out of phase with oneanother. By comparing these two signals, information is obtained whichis representative of the velocity of transmission of the acousticalsignal through a chamber containing the material to be analyzed, andthus of the composition of the material.

The accompanying drawing is a schematic representation of an embodimentof the apparatus of this invention.

Referring now to the drawing in detail, there is shown a chromatographiccolumn which is filled with a material that selectively retards passageof constituents of a mixture to be analyzed. A sample of this mixture isintroduced through a conduit 11 which communicates with a sample valve12. A carrier fluid, which can be either a liquid or a gas, isintroduced through 'a conduit 13 which communicates with valve 12. Theoutlet of valve 12 is connected to the inlet of column 10. The effluentfrom column 10 is directed through a conduit 14 to the inlet of achamber 15. After flowing through chamber 15, this effluent is ventedthrough a conduit 16. An acoustical signal generator 17 is positioned inone end of chamber 15, and an acoustical detector 18 is positioned inthe opposile end of the chamber. Acoustical signals thus pass throughthe chromatographic column effluent in chamber to detector 18.

Valve 12 can be a rotary or diaphragm operated sample valve of the typewell known in the art. The sample mixture initially passes through asample loop in the valve to a vent. When it is desired to introduce apredetermined volume of the sample into column 10, the valve is actuatedso that the carrier fluid forces the trapped sample into the column. Theconstituents of the sample mixture subsequently appear in sequence inthe column effluent. The velocity of propagation of acoustical signalsthrough chamber 15 varies as the composition of the column effluentchanges. A measurement of the changes in the velocity of propagationthus provides information concerning changes in the composition of thecolumn effluent.

First and second capacitors 20 and 21 are connected in seriesrelationship across the output terminals of an oscillator 22. Thejunction between capacitors 20 and 21 is connected to acoustical signalgenerator 17. This generator is also provided with a common groundterminal, not shown. Generator 17 thus provides a series of acousticalpulses at the frequency of oscillator 22. In one specific embodiment ofthis invention employed as a liquid detector, the oscillator can have afrequency of approximately 4.44 megacycles per second. In this sameembodiment, chamber 15 can have a length of about 10 millimeters. Thefirst output terminal of detector 18 is connected to the first terminalof the primary winding of a transformer 23. The second terminal ofdetector 18, not shown, and the second terminal of the primary windingof transformer 23 are connected to ground. A capacitor 24 is connectedacross the primary winding of transformer 23. Capacitors 26 and 27 areconnected in series relationship across the secondary winding oftransformer 23, with the junction between these capacitors beingconnected to ground. The two end terminals of the secondary winding oftransformer 23 are connectd to respective terminals 28 and 29 which areadapted to be engaged selectively by a switch 30. Switch 30 is connectedby a capacitor 31 to the input of an amplifier 32. The output ofamplifier 32 is connected to the set terminal of a flip-flop circuit 33.

An output signal from oscillator 22 is also applied through a phaseadjustment network 34 to the reset terminal of flip-flpp circuit 33. Thefirst output terminal of oscillator 22 is connected to the firstterminals of resistors 35 and 37. The second terminals of theseresistors are connected to ground by a resistor 38 and capacitor 39, anby capacitor 40, respectively. The second terminal of resistor 35 isconnected by a capacitor 42 to the first input of a differentialamplifier 43. A variable resistor 44 is connected in parallel withcapacitor 40. The junction between resistor 37 and capacitor 40 isconnected by a capacitor 45 to the second input terminal of differentialamplifier 43. The output of amplifier 43 is connected by a capacitor 46to the input of an amplifier 47. The output of amplifier 47 is connected to the reset terminal of flip-flop network 33.

The phase of the signal applied to amplifier 47 can be varied byadjusting resistor 44 in phase adjustment network 34. The phase of theoutput signal from detector 18 can be changed by manipulation of switch30. These two adjustments permit the relative phases of the two signalsapplied to flip-flop network 33 to be adjusted relative to one anotherby approximately 360.

Flip-flop network 33 comprises a first transistor 50, the base of whichis connected to the output of amplifier 32. The base of a secondtransistor 50 is connected to the output of amplifier 47. The emittersof transistors 50 and 50' are connected by a common resistor 51 to anegative potential terminal 52. The collectors of transistors 50 and 50'are connected by respective resistors 53 and 53 to ground. Thecollectors of transistors 50 ad 50' are connected to the bases ofrespective transistors 54 and 54'. The emitters of transistors 54 and 54are connected to terminal 52 by respective resistors 55 and 55. Thecollectors of transistors 54 and 54' are connected to ground. The basesof transistors 54 and 54 are connected to the collectors of respectivetransistors 56 and 56'. The emitters of transistors 56 and 56' areconnected by a common resistor 57 to the emitters of transistors 50 and50'. The emitter of transistor 54 is connected to the base of transistor56, and the emitter of transistor 54' is connected in the base oftransistor 56. The emitters of transistors 54 and 54 constitute the twooutputs of the flip-flop circuit.

The input signals to the flip-flop circuit constitute relatively sharppulses, as illustrated. The arrival of a pulse at the base of transistor50 serves to set the flip-flop so as to increase the potential ofnegative polarity tt the emitter of the transistor 54. The later arrivalof a pulse at the base of transistor 50 serves to reset the network sothat there is a decrease in potential at the emitter of transistor 54.This results in a square wave output pulse, the duration of which is afunction of the difference between the times of arrival of the two inputpulses. A corresponding signal appears at the emitter of I} transistor54' except that this signal is 180 out of phase with the signal at theemitter of transistor 54.

The output signals from flip-flop circuit 33 are applied throughrespective low pass filters to the input terminals of a differentialamplifier 60. The emitter of transistor 54 is connected to amplifier 60through resistors 61 and 62. The junction between these resistors isconnected to ground by a capacitor 63. The emitter of transistor 54' isconnected to the second input terminal of amplifier 60 through resistors61 and 62'. The junction between these resistors is connected to groundby a capacitor 63'. A feedback resistor 67 and capacitor 68 areconnected between the output of amplifier 60 and the inverting input ofamplifier 60. Amplifier 60 is provided with a zero adjustment networkwhich includes a potentiometer 64, the end terminals of which areconnected to respective positive and negative potential terminals 65 and66. The contactor of potentiometer 64 is connected to the second inputterminal of amplifier 60 through parallel connected resistor 67'andcapacitor 68'. The output of amplifier 60 is connected to ground acrossa resistor 69. A meter 70 is connected across resistor 69.

Differential amplifier 60 effectively adds the absolute values of thetwo series of input pulses from flip-flop circuit 33. The magnitude ofthe output signal applied to meter 70 is representative of thedifference between the arrival times of the set and reset pulses at thetwo inputs of network 33. If the composition of fluid in chamber 15varies, the velocity of transmission of the acoustical pulses changes.This changes the widths of the output pulses from network 33. Phaseadjustment network 34 and switch permit the apparatus to be adjustedinitially to produce a signal of desired amplitude when a referencefluid is in chamber 15. Actually, the measurement of the D.C. value of asingle series of output pulses from network 33 will provide anindication of changes in composition. The use of differential amplifier60 merely increases the accuracy of the measurement.

While this invention has been described in conjunction with the analysisof the effluent stream from a chromatographic column employing a liquidcarrier fluid, the invention is by no means limited thereto. Gaseousmixtures as well as liquid mixtures can be analyzed, although it may bedesirable in such cases to change the frequency of oscillator 22 tocompensate for differences in the velocity of transmission of theacoustical signals through gas. The detector of this invention can beemployed to measure changes in compositions of fluids from varioussources.

While this invention has been described in conjunction with a presentlypreferred embodiment, it obviously is not limited thereto.

What is claimed is:

1. Apparatus for detecting changes in composition of a fluid comprising:

a chamber adapted to receive the fluid to be tested;

an acousticai signal generator and an acoustical detector positioned insaid chamber in spaced relationship with one another so that fluid inthe chamber occupies the space between said generator and said detector;

an oscillator;

means connecting said oscillator to said signal generator to actuatesame;

a flip-flop circuit having first and second inputs and first and secondoutputs, said first and second outputs generating pulses of the sameconfiguration but out of phase with one another;

means connecting said detector to said first input;

a phase adjustment network;

means connecting sad oscillator to said second input through said phaseadjustment network; and

means connected to said first and second outputs to measure the durationof output pulses from said flip-flop circuit, the duration of suchpulses being representative of the difference between the arrival timesof pulses at the two inputs of said flip-flop circuit, which differenceis representative of the velocity of transmission of acoustical signalsthrough the fluid in said chamber, said means to measure including meansto measure the sum of the absolute values of the output puises from thetwo out puts of said flip-flop circuit.

2. Apparatus for detecting changes in composition of a fluid comprising:

a chamber adapted to receive the fluid to be tested;

an acoustical signal generator and an acoustical detector positioned insaid chamber in spaced relationship with one another so that fluid inthe chamber occupies the space between said generator and said detector;

an oscillator;

means connecting said oscillator to said signal generator to actuatesame;

aflip-flop circuit having first and second inputs and an output;

means connecting said detector to said first input;

a phase adjustment network;

means connecting said oscillator to said second input through said phaseadjustment network; and

means connected to said output to measure the duration of output pulsesfrom said flip-flop circuit, the duration of such pulses beingrepresentative of the difference between the arrival times of pulses atthe two inputs of said flip-flop circuit, which difference isrepresentative of the velocity of transmission of acoustical signalsthrough the fluid in said chamber, said means to measure comprising alow-pass filter to convert output pulses from said flip-flop circuitinto a direct current signal, the amplitude of which is representativeof the duration of the means connecting said detector to said firstinput including means to reverse by the phase of the signal applied tosaid input from said detector;

a phase adjustment network;

means connecting said oscillator to said second input through said phaseadjustment network; and

means connected to said output to measure the duration of output pulsesfrom said flip-flop circuit, the duration of such pulses beingrepresentative of the difference between the arrival times of pulses atthe two inputs of said flip-flop circuit, which difference -isrepresentative of the velocity of transmission of acoustical signalsthrough the fluid in said chamber.

1. Apparatus for detecting changes in composition of a fluid comprising:a chamber adapted to receive the fluid to be tested; an acousticalsignal generator and an acoustical detector positioned in said chamberin spaced relationship with one another so that fluid in the chamberoccupies the space between said generator and said detector; anoscillator; means connecting said oscillator to said signal generator toactuate same; a flip-flop circuit having first and second inputs andfirst and second outputs, said first and second outputs generatingpulses of the same configuration but 180* out of phase with one another;means connecting said detector to said first input; a phase adjustmentnetwork; means connecting sad oscillator to said second input throughsaid phase adjustment network; and means connected to said first andsecond outputs to measure the duration of output pulses from saidflip-flop circuit, the duration of such pulses being representative ofthe difference between the arrival times of pulses at the two inputs ofsaid flip-flop circuit, which difference is representative of thevelocity of transmission of acoustical signals through the fluid in saidchamber, said means to measure including means to measure the sum of theabsolute values of the output pulses from the two outputs of saidflip-flop circuit.
 2. Apparatus for detecting changes in composition ofa fluid comprising: a chamber adapted to receive the fluid to be tested;an acoustical signal generator and an acoustical detector positioned insaid chamber in spaced relationship with one another so that fluid inthe chamber occupies the space between said generator and said detector;an oscillator; means connecting said oscillator to said signal generatorto actuate same; a flip-flop circuit having first and second inputs andan output; means connecting said detector to said first input; a phaseadjustment network; means connecting said oscillator to said secondinput through said phase adjustment network; and means connected to saidoutput to measure the duration of output pulses from said flip-flopcircuit, the duration of such pulses being representative of thedifference between the arrival times of pulses at the two inputs of saidflip-flop circuit, which difference is representative of the velocity oftransmission of acoustical signals through the fluid in said chamber,said means to measure comprising a low-pass filter to convert outputpulses from said flip-flop circuit into a direct current signal, theamplitude of which is representative of the duration of the pulses, andmeans to measure the amplitude of said direct current signal. 3.Apparatus for detecting changes in composition of a fluid comprising: achamber adapted to receive the fluid to be tested; an acoustical signalgenerator and an acoustical detector positioned in said chamber inspaced relationship with one another so that fluid in the chamberoccupies the space between said generator and said detector; anoscillator; means connecting said oscillator to said signal generator toactuate same; a flip-flop circuit having first and second inputs and anoutput; means connecting said detector to said first input includingmeans to reverse by 180* the phase of the signal applied to said inputfrom said detector; a phase adjustment network; means connecting saidoscillator to said second input through said phase adjustment network;and means connected to said output to measure the duration of outputpulses from said flip-flop circuit, the duration of such pulses beingrepresentative of the difference between the arrival times of pulses atthe two inputs of said flip-flop circuit, which difference isrepresentative of the velocity of transmission of acoustical signalsthrough the fluid in said chamber.